1. Field of the Invention
This invention relates to detecting contaminants in seed lots. More specifically, this invention relates to detecting annual or intermediate ryegrass seed or plants in lots of perennial ryegrass seed or plants.
2. Background
Ryegrass is the most commonly used cool season grass for uses such as lawns and golf courses in the temperate regions of the world. Introduced from Europe, perennial ryegrass (Lolium perenne L.) is commonly used for these purposes. Perennial ryegrass, because it overwinters, does not require seeding each year. Accordingly, perennial ryegrass is the most preferred type for a permanent lawn. In contrast to perennial ryegrass, annual ryegrass (L. multiflorum Lam.) is used mostly as a forage crop or as a temporary ground cover. However, annual ryegrass is often present as an undesirable contaminant in perennial ryegrass seed lots. As a consequence of close proximity and due to sexual compatibility, intercrosses of annual and perennial ryegrass occur with some regular frequency, giving rise to intermediate ryegrass (L.×hybridum Hausskn.).
The morphologies of annual and perennial ryegrass seeds are substantially identical. Consequently, visual inspection of samples from seed lots cannot detect the presence or proportion of annual seeds in perennial ryegrass seed lots. Previous attempts to determine the contamination percentage of annual ryegrass seed in seed lots of perennial ryegrass have involved using annuloline as a marker, followed by visual observation of plants in growouts.
Annuloline is an oxazole alkaloid secreted in roots of rye grass plants bearing an allele for expression. Previously, it was believed that the annuloline-secreting allele was present only in annual ryegrass. However, the allele for annuloline secretion has been introgressed into perennial and is often present in intermediate ryegrass varieties. Accordingly, the presence of the allele conferring expression of annuloline is not a reliable indicator of whether a specific ryegrass plant is annual or perennial. Nonetheless, the International Seed Testing Association currently recommends using an annuloline-based test, termed seedling root fluorescence (SRF) and/or a growout test to estimate annual rye grass contamination in perennial ryegrass seed lots. The SRF test has thus been proven unreliable because some perennial ryegrass genotypes express the SRF trait to some degree under certain environmental or test conditions, thereby causing inaccuracies of test results. The SRF test is also laborious and time-consuming, usually requiring two to three weeks to complete. Growout tests, although reliable, are expensive to conduct and may require nearly two months to complete.
There is thus a clear and present need for an alternate, accurate test to distinguish annual and intermediate ryegrass from perennial ryegrass and to estimate the level of annual and intermediate ryegrass seed contamination in perennial ryegrass seed lots.